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Light diffusion plateLight diffusion plate description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060209526, Light diffusion plate. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] This invention relates to a light diffusion plate to be used in a direct type backlight device. BACKGROUND ART [0002] Liquid crystal televisions have attracted attention as a home-use television of 21st century both domestically and internationally in recent years, and it is expected that a demand therefor continues growing in future. [0003] The liquid crystal is not a light emitting device such as a cathode ray tube used in conventional televisions, and it is necessary to dispose a flat light source device called a backlight device behind the liquid crystal. [0004] There are broadly two types of backlight devices. One of them is a so-called edge light type or a side light type backlight device, which has a linear light source, ordinarily a cold cathode tube, disposed beside an optical waveguide. The other is a direct type backlight device wherein a light diffusion sheet called light diffusion plate is disposed in front of a linear light source. [0005] The edge light type backlight device is widely used for displays of a personal computer screens and a notebook type personal computer as well as for car navigation display screens. [0006] The direct type backlight device has widely been used for the reasons of a simple structure and brightness, but the edge light type backlight device has grubbed the market share from the direct type backlight device since the direct type backlight device is too thick to meet the demand of reducing the thickness and uses a lot of electricity for plural light sources. [0007] However, since liquid crystal televisions today require brightness as is the case with the cathode ray tube, the direct type backlight device which realizes high brightness due to its structure of directly transmitting light from the light source is attracting attention again. Particularly, use of the direct type backlight device in large screen such as liquid crystal televisions having over 20 inches is rapidly increasing. [0008] The direct type backlight device is schematically shown in FIG. 1. [0009] In the direct type backlight device, a light scattering functional sheet called a light diffusion plate is disposed in front of a linear light source in order to scatter light of the linear light source, and plural optical films having a light condensing function and a polarizing function are laminated in order to emit light effectively. [0010] The light diffusion plate is used for transmitting and scattering light; erasing a so-called lamp image that is a phenomenon that a shape of the linear light source, particularly its linear outline is shown through; and decreasing and uniformizing irregularity in brightness on a screen. Whereas, when the light diffusion property of the light diffusion plate excessively functionate, the light to be transmitted is weakened to darken the screen, which is problematic. The light diffusion plate has heretofore been required to achieve high transmittance property and high diffusion property which are conflicting optical properties. [0011] Also, it has been considered important to refine irregularity on a surface of the light diffusion plate in order to prevent the high diffusion and the lamp image of linear light source. The irregularity on surface is represented as a degree of brilliancy. The surface is smooth as a mirror when a value of the degree of brilliancy is high, while the surface has fine irregularity and reduced in reflection when the degree of brilliancy is low. That is, it has been considered that the high diffusion property is achieved when the degree of brilliancy is low, and methods of reducing the degree of brilliancy have been developed. In fact, the degree of brilliancy of the surface of the conventional light diffusion plates is ordinarily 10% or less, and a non-reflecting light diffusion plate having a fine surface of degree of brilliancy of 1% or 0%, which is the same as the degree of brilliancy of a paper, has been used as the light diffusion plate for the direct type backlight (see Patent Documents 1 to 3, for example). [0012] The above described technologies have realized an increase in brightness of the direct type backlight device to be about twice as that of the edge light type backlight device using an optical waveguide; however, since peak brightness of the direct type backlight device is still lower than that of the cathode ray tube, there is a demand for a further improvement in brightness. [0013] [Patent Document 1] JP 1-172801 A [0014] [Patent Document 2] JP 2-194058 A [0015] [Patent Document 3] JP 11-5241 A DISCLOSURE OF THE INVENTION [0016] An object of this invention is to provide a light diffusion plate realizing high brightness for a direct type backlight device. [0017] Though it has been considered that brightness of a surface of a light diffusion plate is increased by lowering a degree of brilliancy of the surface to refine the surface, the present inventors have found that the brightness is largely improved by increasing the degree of brilliancy contrary to the conventional idea. With this finding, the present invention is accomplished. [0018] An object of this invention is achieved by producing a light diffusion plate and a direct type backlight device described below. [0019] 1. A light diffusion plate comprising: a light transmitting thermoplastic resin; and a light diffusing agent, wherein the light diffusing agent is contained in an amount of 0.2 to 10% by weight with respect to the total weight of the light diffusion plate, wherein a degree of brilliancy of at least one surface of the light diffusion plate is from 20 to 70%. [0020] 2. The light diffusion plate according to item 1, which comprises: a base material layer and; a coating resin layer formed on at least one surface of the base material layer, wherein the base material layer and the coating resin layer each comprises the light transmitting thermoplastic resin and the light diffusing agent. [0021] 3. The light diffusion plate according to item 2, wherein an amount of the light diffusing agent contained in the coating resin layer is 1 to 10% by weight with respect to a weight of the coating resin. Continue reading about Light diffusion plate... Full patent description for Light diffusion plate Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Light diffusion plate patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Light diffusion plate or other areas of interest. ### Previous Patent Application: Display having indirect lighting structure Next Patent Application: Ito film treated by nitrogen plasma and the organic luminescent device using the same Industry Class: Illumination ### FreshPatents.com Support Thank you for viewing the Light diffusion plate patent info. 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